The present invention relates to a semiconductor device and a manufacturing method for the same, and more particularly to an improvement in performance and an increase in the yield of a power semiconductor device.
An element using a repeating microscopic structure of p-type and n-type layers wherein an electric field relaxation phenomenon called the RESURF (REduced SURface Field) effect is applied in place of the uniform n-type drift layer of a conventional MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor) has been proposed in, for example, U.S. Pat. No. 6,040,600. In this element a low ON resistance is obtained in the ON condition due to the n-type drift layer of which the impurity concentration is higher than the concentration of the uniform n drift layer in the conventional structure by approximately one order while in the OFF condition the entire electric field is relaxed due to a three-dimensional multiple RESURF effect of n/p layers. Thereby, a withstand voltage several times as large as the main withstand voltage conventionally obtained by a high concentration single n-type drift layer alone can be implemented and, in principle, an STM (Super Trench power MOS-FET) structure that can obtain a value lower than the Si limitation (Ron, sp=5.93xc3x9710xe2x88x929 BV2.5, wherein specific resistance is proportional to the main withstand voltage to the power of 2.5) wherein the relationship between the main withstand voltage and the specific ON resistance is limited can be obtained.
In an actual element, however, this repeating microscopic structure of p-type and n-type layers cannot be repeated infinitely in an edge portion of the chip and, therefore, there is a problem wherein a drop in the main withstand voltage is great in a xe2x80x9cterminationxe2x80x9d portion of a termination structure where the repetition ends. In the following, a prior art and problem thereof are described from such a point of view.
FIG. 148 is a cross sectional view schematically showing the first configuration of a semiconductor device according to a prior art and shows a configuration that corresponds to a case where a MOS-FET is posited as a concrete active element structure. In reference to FIG. 148, an nxe2x88x92 epitaxial layer 102 is formed on the first main surface side of an n+ drain region 101 of the MOS-FET. A pn-repeating structure wherein n-type drift regions 103 and p-type impurity regions 104 are repeated in alternation is formed within this nxe2x88x92 epitaxial layer 102.
Here, though the vicinity of the center of this element having the pn-repeating structure is omitted for the purpose of simplification of the description, conventionally a combination of several hundreds to several tens of thousands of repeated pairs of n-type drift regions 103 and p-type impurity regions 104 exists in this portion. The n-type impurity concentration of n-type drift region 103 and the p-type impurity concentration of p-type impurity region 104 in each pair are set at substantially the same level.
A p-type body region 105 is formed on the first main surface side of p-type impurity region 104. This p-type body region 105 is also located on, at least, a portion of n-type drift region 103 on the first main surface side so as to form a main pn junction with n-type drift region 103. An n+ source region 106 of a MOS-FET and a p+ contact region 107 for making a low resistance contact with p-type body region 105 are formed side by side in the first main surface within this p-type body region 105.
A gate electrode 109 is formed above the first main surface so as to face p-type body region 105 located between n-type drift region 103 and n+ source region 106 via a gate insulating film 108. When a positive voltage is applied to this gate electrode 109, p-type body region 105, which faces gate electrode 109, is inverted to an n-type so that a channel region is formed.
A source electrode 110 made of a material including aluminum (Al), for example, is formed on the first main surface so as to be electrically connected to n+ source region 106 and p+ contact region 107.
A drain metal wire 111 is formed on the second main surface so as to contact n+ drain region 101.
Here, in the actual element, the source electrode part is electrically connected to n+ source region 106 and p+ contact region 107 through a contact hole provided in an interlayer insulating film on the first main surface and via a barrier metal. In the present application, however, this portion is not important and, therefore, the source electrode part is simplified and expressed using solid lines throughout all of the drawings.
In addition, though n+ drain region 101 is several times to several tens of times thicker than the effective element portion in the actual element, n+ drain region 101 is expressed as thinner than the effective element portion in the drawings for the purpose of simplification. In addition to the above, scales, ratios of dimensions, and the like, are deformed in order to simplify the expression and, therefore, the respective dimensions in the drawings are not necessarily precise.
A multiple guard ring structure made of p-type impurity regions 115, for example, is provided as a termination structure of the pn-repeating structure.
In this configuration, n-type drift regions 103 and p-type impurity regions 104, respectively, have substantially the same impurity concentration in the center portion and edge portions of the pn-repeating structure.
FIG. 149 is a cross sectional view schematically showing the second configuration of the semiconductor device according to the prior art. In reference to FIG. 149, an nxe2x88x92 epitaxial layer 102 has a buried multi-layer epitaxial structure and a p-type impurity region 104 is formed of a plurality of p-type regions 104a that are integrated in the depth direction of the semiconductor substrate in this configuration. In this configuration, p-type impurity regions 104, respectively, have the same impurity concentration in the center portion and edge portions of the pn-repeating structure.
Here, the concentration distribution in the upward and downward directions of each p-type impurity region 104 is an intrinsic structure and this is a concentration distribution due to the manufacturing method, which has no bearing on the concentration gradient in the part in the lateral direction discussed in the present invention. In addition, though in the drawing the concentration gradient in the upward and downward directions is depicted in only two stages for the purpose of simplification, in practice this concentration sequentially changes.
A manufacturing method according to this prior art is characterized in that nxe2x88x92 epitaxial layer 102, having a comparatively high concentration to the extent that the concentration thereof is balanced with that of the p-type layers, is used for the purpose of simplifying the process of formation of the buried layers. A heat treatment is carried out after forming p-type buried diffusion layers 104a within nxe2x88x92 epitaxial layer 102 in such a manner and, therefore, p-type impurity region 104 becomes of a form well-known in Japan as xe2x80x9cround sweet balls of confectionary on a skewer.xe2x80x9d
FIG. 150 is a cross sectional view schematically showing the third configuration of the semiconductor device according to the prior art. In reference to FIG. 150, n-type drift regions 103 and p-type impurity regions 104 form pairs and a trench 123 filled in with a filling 124 is arranged between the members of each combined pn pair in this configuration.
FIG. 151 shows the appearance of electrical field concentration in the structure corresponding to this FIG. 150. The dark portion in this figure indicates a portion of high electrical field concentration and it is seen that an electrical field concentrates on portions (regions shown by arrows) wherein the pn-repeating structure ends.
Here, in this FIG. 151, an FP (Field Plate) structure is adopted for the termination structure portions instead of the multiple guard ring called an FLR (Field Limiting Ring) or an FFR (Floating Field Ring).
Here, the other parts of the above described configurations shown in FIGS. 149 and 150 are approximately the same as in the configuration shown in FIG. 148 and, therefore, the same symbols are attached to the same members, of which the descriptions are omitted.
As described above, according to the first to third prior arts there are structures wherein conventional termination structures such as a guard ring, an LFR, a JTE (Junction Termination Extension) and an FP are combined in the portions wherein pn-repeating structures end. By combining such termination structures, however, only a withstand voltage far lower than the high withstand voltage obtained within the cell in the center portion of the pn-repeating structures can be obtained in portions wherein the pn-repeating structure ends. Therefore, though the element operates, there is a problem wherein the trade-off relationship between the main withstand voltage and the ON resistance does not improve.
In addition, the content of the following Prior Art 1 has been announced as a method for preventing the loss of the high withstand voltage of the main cell portion by setting a specific concentration of the p-type layers and of the n-type layers outside of the portions wherein the pn-repeating structures ends. According to this technique, however, there is a problem wherein implementation is difficult due to the reasons described below.
The above described Prior Art 1 is described in xe2x80x9cJunction Termination Technique for Super Junction Devicesxe2x80x9d that was announced in, for example, ISPSD 2000 (International Symposium on Power Semiconductor Devices and ICs) of CPES (Center for Power Electronics Systems), Virginia Polytechnic Institute and State University.
This Prior Art 1 shows improvement of the termination structure itself in the pn-repeating structure.
In addition, the structure shown in FIG. 152 is shown in the above described Prior Art 1. In reference to FIG. 152, a region of which the effective conductive type and concentration can be regarded as those of a low concentration pxe2x88x92 region in a fan form of a quarter of a circle having a radius of R of the thickness (depth) of an n layer is formed from a portion wherein the repetition of p layers 204 and n layers 203 ends. However, a pxe2x88x92 region cannot actually be formed to have such a concentration distribution. Therefore, it is necessary for the concentration distribution of the effective pxe2x88x92 region to have an attenuation curve as shown in FIG. 153.
In order to implement this, a configuration is used wherein the concentration and the width of n-type regions 203 are constant while the concentration of p-type regions 204 is constant and the widths thereof are changed such as in the SJT (Super Junction Termination) structure shown in FIG. 154. Thereby, the same effects as of the changing of the effective concentration can be obtained according to the description of Prior Art 1.
In addition, the only requirements at this time are a form wherein the equipotential surfaces are aligned in fans at equal intervals as shown in FIG. 155 and a zigzag electrical field intensity distribution that is exposed to the surface wherein the peaks and the troughs have the same height and depth, respectively.
In addition, in this Prior Art 1 each of the concentrations of pi regions 204 and ni regions 203 are posited as being uniform within the single diffusion layer in the upward, downward, leftward and rightward directions. There is a problem, however, wherein the original effects of Prior Art 1 cannot easily be exercised when the formula for the relationship of the pn concentration ratio is not fulfilled in the case that the absolute values of the concentration greatly change or when the description of such a relationship becomes extremely complex so that the precision of proximity is reduced.
Concretely, there is a description that xe2x80x9calong the SJT surface, . . . in the following calculation.xe2x80x9d in right column of page 2 to the left column of page 3 in the main body of Prior Art 1. In this description the volume represented by the concentration and the width of each portion may be set so as to satisfy equation (5) in Prior Art 1 so that the electrical field distribution closest to the surface does not reach to the critical breakdown electrical field.
In other words, this Prior Art 1 discloses the design of the entirety of the element in a form that includes the termination structure by literally extending the super junction structure of the repeating cell portions to the termination structure portions in some manner according to SJT, that is to say, xe2x80x9cSuper Junction Termination structure,xe2x80x9d wherein a repeating cell portion in the center and a termination structure have a one-to-one correspondence so as to be indivisible having a very limitative structure while xe2x80x9cmanner of connectionxe2x80x9d of a repeating cell portion to a general termination structure portion is described in the present invention, which is essentially different from the above.
In the case that the distribution required for the p-type acceptor concentration distribution in the moving radius direction in FIG. 153 is formed according to the repetition of pn layers, the electrical field distribution closest to the surface becomes of a zigzag form and, in the case that the peaks and troughs all have the same value, the maximum withstand voltage can be obtained. Therefore, in the case that the all of the concentrations of n and p regions 203 and 204 are made uniform so that the equipotential surfaces (lines) distribute in fan forms at equal intervals, as shown in FIG. 155, it is necessary to carry out an adjustment of the width of each of the regions 203 and 204.
In addition, SJT is considered to be impractical because it has the following two problems.
First, concentration regulation for forming an SJT structure is too complicated and it is necessary to apply an interval design that agrees with the concentration arrangement of the repeating cell portions that are different from the termination structure portions to the SJT part after examining the arrangement in detail before carrying out the actual design and, in addition, it is physically and mechanically difficult to fabricate a semiconductor chip structure to include terminal edges. On the other hand, the present invention has the advantage that both design and manufacturing method are simple because the relative concentrations in the vicinity of the terminal edges of the repeating cell portions may be adjusted using comparatively simple arithmetic.
Secondly, an SJT structure can only be implemented in the case of manufacture by means of a buried multi-layer epitaxial growth method and lacks versatility in that it cannot be actually manufactured in the case wherein a trench sidewall diffusion is used.
Furthermore, as described in the main body of Prior Art 1, there is a problem wherein this technique lacks versatility in that it is impossible to apply this technique in an element structure wherein a trench system is applied due to restrictions of the manufacturing technology even though the application to a multi-layer epitaxial structure is, in principle, possible.
Next, the technology disclosed in U.S. Pat. No. 5,438,215 is described as prior art 2 in FIG. 156.
In reference to FIG. 156, a vertical-type MOS-FET has inside region 301 that is doped so as to be a low level n-type. A base region 303 of the opposite conductive type (p) is provided in the upper side surface 302 of the semiconductor substrate. A source region 304 of the first conductive type (n) is buried within base region 303. A gate electrode 308 is arranged above surface 302 so as to be insulated from the surface. A drain region 307 that is highly doped so as to be of the same conductive type as inside region 301 is provided in the surface 306 on the opposite side.
Auxiliary semiconductor regions 311 and 312 are arranged in a range of the space-charge region that spreads at the time of reverse voltage application within the inside region 301. At least two regions 211 of a conductive type opposite to that of the inside region are provided. Auxiliary regions 312 having the same the same conductive type (n) as inside region 301 and being more highly doped than the inside region arranged between regions 311. The auxiliary regions are surrounded from all directions by a single region. This single region is of the same conductive type as the inside region, as well as regions 312, and is more highly doped than the inside region.
Though in this configuration a portion, wherein an active cell is formed, is buried in nxe2x88x92 region 301, which has a low concentration, the impurity concentration of this outer peripheral portion is not specifically described and only the method of formation of a cell portion is discussed.
In addition, in general the impurity concentration of a portion wherein a pn-repeating structure is not formed in this Prior Art 2 is presumed to be set at the impurity concentration that is reverse calculated from a value obtained by adding a manufacturing margin to the element withstand voltage set for the power MOS-FET of a conventional structure (structure that does not have pn repetition). However, that leads the electrical field distribution in the termination structure portions in the pn-repeating structure to become triangular so as to differ from an electrical field distribution in a trapezoidal form that is implemented in the cell portion. Therefore, in the same manner as in the above described Prior Art 1, the difference in the electrical field distribution between the inside of repeating cells and the termination structure portions becomes greater so that there is a problem wherein a high withstand voltage, which is essentially obtained in a cell portion, cannot be implemented although the relationship between the main withstanding voltage and the ON resistance is improved in comparison with the conventional MOS-FET structure.
An object of the present invention is to provide a structure which improves the trade-off relationship between the main withstanding voltage and the ON resistance, and a manufacturing method capable of implementing such a structure in a semiconductor device based on a three-dimensional multiple RESURF effect.
A semiconductor device of the present invention is a semiconductor device having a repeating structure, wherein a structure where a first impurity region of a first conductive type and a second impurity region of a second conductive type are aligned side by side, is repeated twice or more in a semiconductor substrate of the first conductive type, characterized in that a low concentration region, which is either the first or the second impurity region located at the outermost portion in the repeating structure, has the lowest impurity concentration or has the least generally effective charge amount from among all of the first and second impurity regions forming the repeating structure.
According to the semiconductor device of the present invention a portion of the concentration of the outermost portion in the repeating structure is converted to have a concentration lower than the center portion and, thereby, the xe2x80x9cmitigating regionxe2x80x9d that gradually mitigates the strong xe2x80x9cthree-dimensional multiple RESURF effectxe2x80x9d used in the repeating cell portion in the center portion is provided so that the connection with a conventional so-called xe2x80x9ctermination structurexe2x80x9d portion formed of a guard ring or a field plate is made easier and the main withstanding voltage drop caused by xe2x80x9cmismatchxe2x80x9d in the connection between the strong xe2x80x9cthree-dimensional multiple RESURF effectxe2x80x9d portion and a so-called xe2x80x9ctermination structurexe2x80x9d portion can be restricted.
In the above described semiconductor device the impurity concentration of the low concentration region is preferably no lower than 30% and no higher than 70% of the impurity concentration of the high concentration region that is either the first or second impurity region located closer to the center portion of the repeating structure than is the low concentration region.
By adjusting the impurity concentration in such a manner, it becomes possible to adjust the concentration gradient from the center portion of the pn-repeating structure to the first conductive region of the semiconductor substrate to be in a range that can be regarded as being continuous.
In the above described semiconductor device, the impurity concentration of the middle concentration region, which is of the above described first or second impurity region located between the low concentration region and the high concentration region, is higher than the impurity concentration of the low concentration region and is lower than the impurity concentration of the high concentration region.
Furthermore, by providing a the middle concentration region in such a manner, it becomes possible to continuously change the concentration gradient from the center portion of the pn-repeating structure to the first conductive region of the semiconductor substrate.
In the above described semiconductor device, the semiconductor substrate preferably has a first main surface and a second main surface facing each other wherein a third impurity region of the second conductive type is formed in, at least, a portion of at least one of the plurality of the first impurity regions on the first main surface side that forms the repeating structure so as to form a main pn junctions with the first impurity regions and a fourth impurity region of the first conductive type is formed on the second main surface side of the repeating structure.
Thus, the present invention can be applied to an element having a vertical-type structure.
In the above described semiconductor device, the third impurity region that forms the main pn junctions with the first impurity regions is preferably a body region of an insulating gate-type field effect transistor portion.
Thus, the present invention can be applied to an element having a MOS-FET.
In the above described semiconductor device, the low concentration regions located at the outermost portion in the repeating structure do not form active elements.
Thereby, the withstand voltage alone can be maintained in the low concentration regions having a concentration gradient that tends to be unstable at the time of switching operation without forming an element, such as a MOS-FET, so that stable switching operation can be obtained.
In the above described semiconductor device, a third impurity region of the second conductive type formed in, at least, a portion of the upper portion of the first impurity region close to an end that extends in one specific direction, a fourth impurity region of the first conductive type formed in, at least, a portion of the upper portion of the first impurity region close to an end in the direction opposite to the above described one specific direction, a first electrode electrically connected to the third impurity region and a second electrode electrically connected to a fourth impurity region are further provided, wherein the first and second electrodes are both formed on the first main surface.
Thus, the present invention can be applied to an element having a lateral-type structure.
In the above described semiconductor device, the semiconductor substrate preferably has a first main surface and a second main surface that face each other and has a plurality of trenches in the first main surface, wherein the repeating structure has a structure where a structure in which the first and second impurity regions are arranged side by side with a trench located in between is repeated twice or more.
Thus, the present invention can be applied to an element having a trench, for example, an ST (Super Trench) type element.
In the above described semiconductor device, the impurity concentration of the low concentration region is preferably no lower than 30% and no higher than 70% of the impurity concentration of the high concentration region, which is the first or second impurity region, that is located closer to the center portion of the repeating structure than is the low concentration region.
By adjusting the impurity concentration in an element having a trench in such a manner, it becomes possible to adjust the concentration gradient from the center portion of the pn-repeating structure to the first conductive type region of the semiconductor substrate to be in a range such that the concentration gradient can be regarded as being continuous.
In the above described semiconductor device, the impurity concentration of the middle concentration region, which is either the first or the second impurity region, located between the low concentration region and the high concentration region is preferably higher than the impurity concentration of the low concentration region and lower than the impurity concentration of the high concentration region.
Furthermore, by providing the middle concentration region in an element having a trench in the above described manner, it becomes possible to continuously change the concentration gradient from the center portion of the pn-repeating structure to the first conductive type region of the semiconductor substrate.
In the above described semiconductor device, a first impurity region is formed on one side of a mesa portion of a semiconductor device surrounded by a plurality of trenches and a second impurity region is formed in the surface of the other side and a third impurity region of the second conductive type is formed in, at least, a portion of the above described first main surface side of the first impurity region so that the first impurity region and the main pn junction are formed.
Thus, the present invention can be applied to an element having an ST-type mesa region.
In the above described semiconductor device, the third impurity region forming a pn junction primarily with the first impurity region is a body region of an insulating gate-type field effect transistor portion.
Thus, the present invention can be applied to an ST-type element having a MOS-FET, that is to say, to an STM (Super Trench power MOS-FET).
In the above described semiconductor device, the low concentration region located at the outermost portion of the repeating structure preferably does not form a passive element.
Thereby, withstand voltage alone can be maintained in the ST-type element without forming an element, such as a MOS-FET, in a low concentration region having a concentration gradient which easily becomes unstable at the time of switching operation so that a stable switching operation can be obtained.
In the above described semiconductor device, the trench positioned at the outermost part of the plurality of trenches is a first trench in a dotted line form having a surface pattern in a dotted line form wherein a plurality of first holes are arranged at intervals in a predetermined direction in the first main surface and the low concentration region is formed so as to be located along one of the sidewalls of the first trench of a dotted line form.
Thus, the present invention can be applied to an element having a trench in a dotted line form, that is to say, to an element having a DLT (Dotted Line Trench) so that the manufacturing process can be simplified.
The total of the length of the sidewalls on one side of the first main surface of a plurality of first holes forming the first trench of a dotted line form is preferably no lower than 30% and no more than 70% of the length of the sidewalls on one side in the first main surface of the trench continuously extending along a location closer to the center portion than the first trench of a dotted line form.
Thus, in an element having the DLT structure, the length and the intervals of the holes of the trench of the dotted line form are adjusted and, thereby, the impurity concentration of the low concentration region can be adjusted. Thereby, it becomes possible to adjust the concentration gradient from the center portion of the pn-repeating structure to the first conductive type region of the semiconductor substrate to be in a range that can be regarded as continuous.
In the above described semiconductor device, the trench located between the first trench of a dotted line form and the continuously extending trench is preferably a second trench of a dotted line form having a surface pattern in a dotted line form wherein a plurality of second holes are arranged at intervals in a predetermined direction in the first main surface and the sum of length of the sidewalls on one side in the first main surface of the plurality of second holes that form the second trench of a dotted line form is greater than the sum of length of the sidewalls on one side in the first main surface of the plurality of first holes that form the first trench of a dotted line form and is less than the length of the sidewall on one side in the first main surface of the continuously extending trench in the location closer to the center portion than the second trench of a dotted line form.
Thus, the trenches of dotted line forms are provided in a step-by-step manner in the element having the DLT structure and, thereby, the concentration gradient can be regarded as being continuous from the center portion of the pn-repeating structure to the first conductive type region of the semiconductor substrate.
In the above described semiconductor device, the first impurity region is preferably formed on one of the sides of the mesa portion of the semiconductor device surrounded by a plurality of trenches and the second impurity region is formed on the other of the sides and the third impurity region of the second conductive type is formed in, at least, a portion on the first main surface side of the first impurity region so as to form a main pn junction with the first impurity region.
Thus, the present invention can be applied to an element having a DLT structure and having an ST-type mesa region.
In the above described semiconductor device, the third impurity region, which forms the main pn junction with the first impurity region, is a body region of an insulating gate-type field effect transistor portion
Thus, the present invention can be applied to an element having a MOS-FET in an ST-type type element having a DLT structure, that is to say, to an STM (Super Trench power MOS-FET).
In the above described semiconductor device, the low concentration region located at the outermost portion of the repeating structure preferably does not form an active element.
Thereby, the withstand voltage alone can be maintained without forming an element, such as a MOS-FET, in the low concentration region having a concentration gradient that tends to become unstable at the time of switching operation in an ST-type element having a DLT structure so that a stable switching operation can be obtained.
In the above described semiconductor device, the semiconductor substrate preferably has a first main surface and a second main surface facing each other and has a plurality of trenches including first and second trenches adjoining each other in the first main surface wherein a structure where a first impurity region is formed in each of the two sidewalls of the first trench and a second impurity region is formed in each of the two sidewalls of the second trench is repeated twice or more.
Thus, the present invention can be applied to an element having a twin trench structure.
In the above described semiconductor device, the impurity concentration of the low concentration region is no lower than 30% and no higher than 70% of the impurity concentration of the high concentration region that is either the first or second impurity region located closer to the center portion in the repeating structure than the low concentration region.
Thus, in an element having a twin trench structure, it becomes possible to adjust the impurity concentration of the low concentration region and, thereby, to adjust the concentration gradient from the center portion in the pn-repeating structure to the first conductive type region of the semiconductor substrate to be in a range that is regarded as being continuous.
In the above described semiconductor device, the impurity concentration of the middle concentration region, which is either the first or second impurity region, located between the low concentration region and the high concentration region is preferably higher than the impurity concentration of the low concentration region and is lower than the impurity concentration of the high concentration region.
Thus, trenches of dotted line forms are provided in a side by side manner in an element having a twin trench structure and, thereby, the concentration gradient from the center portion of the pn-repeating structure to the first conductive type region of the semiconductor substrate can be regarded as being continuous.
In the above described semiconductor device, a first impurity region is preferably formed on one side of the mesa portion of the semiconductor substrate surrounded by a plurality of trenches, a second impurity region is formed on the other side and a third impurity region of the second conductive type is formed on, at least, a portion of the first main surface side of the first impurity region so as to form a main pn junction with the first impurity region.
Thus, the present invention can be applied to an element having twin trench structure.
In the above described semiconductor device, the third impurity region forming the main pn junction with the first impurity region is preferably a body region of an insulating gate-type field effect transistor portion.
Thus, the present invention can be applied to an element having a MOS-FET in an element having a twin trench structure.
In the above described semiconductor device, the low concentration region located at the outermost portion of the repeating structure preferably does not form an active element.
Thereby, withstand voltage alone can be maintained without forming an element, such as a MOS-FET, in the low concentration region having a concentration gradient that tends to become unstable at the time of switching operation in an element having a twin trench structure so that a stable switching operation can be obtained.
In the above described semiconductor device, the trench located at the outermost portion of the plurality of trenches is the first trench of a dotted line form having a surface pattern of a dotted line form wherein a plurality of first holes are arranged at intervals in a predetermined direction in the first main surface and the low concentration region is formed so as to be located on one of the sidewalls of the first trench of a dotted line form.
Thus, the present invention can be applied to an element having a twin trench structure and having a DLT structure so that the manufacturing process can be simplified.
In the above described semiconductor device, the sum of the lengths of the sidewalls on one side in the first main surface of the plurality of first holes forming the first trench of a dotted line form is no greater than 30% and no less than 70% of the length of the sidewall on one side in the first main surface of the trench that extends continuously in a location closer to the center portion than the first trench of a dotted line form.
Thus, in an element having a twin trench structure and having a DLT structure, by adjusting the length and intervals of the holes of the trench of a dotted line form, the impurity concentration of the low concentration region can be adjusted. Thereby, it becomes possible to adjust the concentration gradient from the center portion of the pn-repeating structure to the first conductive region of the semiconductor device to be in a range that is regarded as being continuous.
In the above described semiconductor device, a trench located between the first trench of a dotted line form and the continuously extending trench is a second trench of a dotted line form having a surface pattern of a dotted line form wherein a plurality of second holes are arranged at intervals in a predetermined direction in the first main surface and the sum of the lengths of the sidewalls on one side of the plurality of second holes forming the second trench of a dotted line form in the first main surface is greater than the sum of the lengths of the sidewalls on one side of the plurality of first holes forming the first trench of a dotted line form and is smaller than the length of the sidewall on one side of the continuously extending trench that is closer to the center portion than the second trench of a dotted line form in the above described first main surface.
Thus, by providing trenches of a dotted line form in a step-by-step manner in the element having a twin trench structure and having a DLT structure, the concentration gradient from the center portion of the pn-repeating structure to the first conductive type region of the semiconductor substrate can be regarded as being continuous.
In the above described semiconductor device, a first impurity region is preferably formed on one side of the mesa portion of the semiconductor substrate surrounded by the plurality of trenches, a second impurity region is formed on the opposite side of the mesa portion and a third impurity region of the second conductive type is formed in, at least, a portion on the above described first main surface side of the first impurity region so as to form a main pn junction with the first impurity region.
Thus, the present invention has a twin trench structure and a DLT structure and can be applied to an element having an ST-type mesa region.
In the above described semiconductor device, the third impurity region forming a main pn junction with the first impurity region is preferably a body region of an insulating gate-type field effect transistor portion.
Thus, the present invention can be applied to an element having a MOS-FET in an element having a twin trench structure and a DLT structure.
In the above described semiconductor device, the low concentration region located at the outermost portion of the repeating structure preferably does not form an active element.
Thereby, the withstand voltage alone can be maintained without forming an element, such as a MOS-FET, in the low concentration region having a concentration gradient that tends to become unstable at the time of switching operation in an ST-type element having a twin trench structure and a DLT structure so that a stable switching operation can be obtained.
A manufacturing method for a semiconductor device of the present invention is characterized in that the low concentration region and other first and second impurity regions are formed by independently changing the concentration so that the low concentration region, which is either the first or second impurity region located at the outermost portion of the repeating structure, has the lowest impurity concentration or has the least generally effective charge amount from among all of the first and second impurity regions forming the repeating structure in a manufacturing method for a semiconductor device having a repeating structure wherein a structure where a first impurity region of a first conductive type and a second impurity region of a second conductive type are aligned side by side is repeated twice, or more, in a semiconductor substrate of the first conductive type
According to the manufacturing method for a semiconductor device of the present invention, the outermost portion of the repeating structure has a concentration lower than that of the center portion and, thereby, the concentration of i layer of a pin diode formed of the repeating structure and the region of the first conductive type of the semiconductor substrate can be lowered. Thereby, it becomes possible to adjust the concentration of the i layer so that the withstand voltage obtained at the outermost portion of the repeating structure becomes greater than the withstand voltage obtained in the center portion. Therefore, an increase in the withstand voltage at a cell portion can be achieved, in contrast to the prior art.
In the above described manufacturing method for a semiconductor device, the low concentration region and other first and second impurity regions are preferably formed by means of ion implantation and heat treatment in order to independently control the concentration so as to form the low concentration region and other first and second impurity regions of which the concentrations have been independently changed.
Because of the formation using ion implantation in such a manner, the process can be simplified and the low concentration region can be formed under effective control. In addition, this method is suitable for a manufacturing method for a low withstand voltage element.
In the above described manufacturing method for a semiconductor device, the low concentration region and other first and second impurity regions are preferably formed by means of ion implantation and multi-stage epitaxial growth in order to independently control the concentration so as to form the low concentration region and other first and second impurity regions of which the concentrations have been independently changed.
Since multi-stage epitaxial growth is used, epitaxial layers can, in principle, be layered infinitely. Accordingly, this method is suitable for a manufacturing method for high withstand voltage element.
In the above described manufacturing method for a semiconductor device, the low concentration region and other first and second impurity regions are favorably formed by independently changing the concentrations and, therefore, the above described low concentration region and other first and second impurity regions have independently changed concentrations and are formed by means of ion implantation wherein implantation energy is changed according to multi-stages.
Since, a multi-stage ion implantation is used, the process can be simplified and the low concentration region can be formed under effective control. In addition, this method is suitable for a manufacturing method for a low withstand voltage element.
In the above described manufacturing method for a semiconductor device, impurity ions injected from the first openings in a mask for ion implantation preferably form the first and second impurity regions, other than the low concentration region, while impurity ions injected from the second openings, of which the total area of the openings is smaller than that of the first openings, form the low concentration region in order to independently change the concentrations at the time of the formation of the low concentration region and other first and second impurity regions.
Thus, openings, of which the areas of the openings differ, are used and, thereby, high concentration regions are low concentration regions can be formed at the same time through a single ion implantation process so that simplification of the process can be achieved.
In the above described manufacturing method for a semiconductor device, the second openings preferably have a configuration wherein a plurality of microscopic openings separated from each other are densely arranged so that impurity ions injected from each of the plurality of microscopic openings are integrated by applying a heat treatment so as to form a finished low concentration region of which the average impurity concentration is lower than that of the other first and second impurity regions.
Thus by using the configuration wherein a plurality of microscopic openings separated from each other are densely arranged, the openings, of which the areas of the openings differ, can easily be formed.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of creating one, or more, trenches and a trench of a dotted line form having a surface pattern of a dotted line form in the first main surface at the same time by arranging the trench of a dotted line form so as to be located along the outside of the above one, or more, trenches wherein a plurality of first holes are arranged at intervals in a predetermined direction and the step of forming a low concentration region on the one sidewall of the trench of a dotted line form and the other first and second impurity regions on one of the sidewalls of the above one, or more, trenches at the same time by simultaneously implanting ions in the above one, or more, trenches and in one of sidewalls of respective trenches of a dotted line form.
Thus, the trenches of a dotted line form are used in the STM structure and, thereby, a high concentration region and a low concentration region can be simultaneously formed by means of a single ion implantation step so that simplification of the process can be achieved.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of creating two, or more, trenches in the first main surface of the semiconductor substrate, the step of implantation of impurities in order to form the first and second impurity regions and the step of forming a low concentration region by substantially lowering the concentration of the impurities that have already been implanted through the ion implantation of impurities of a conductive type opposite to the already implanted impurities in the one sidewall of the trench located at the outermost portion.
Thus, in the STM structure the concentration of the impurity region at the outermost portion in the repeating structure can be lowered by means of counter doping.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of creating one, or more, trenches in the first main surface of the semiconductor substrate, the step of ion implantation with a first implantation amount in order to form first or second impurity regions on one side of the respective sidewalls of the above one, or more, trenches, the step of creating a new trench at the outermost portion outside of the above one, or more, trenches in the condition wherein each of the above one, or more, trenches is filled in with a filling layer and the step of ion implantation with a second implantation amount smaller than the first implantation amount in order to form a low concentration region on one sidewall of the trench at the outermost portion.
Thus, the trenches in the center portion and at the outermost portion in the pn-repeating structure can be separately created and ion implantations can be separately implemented in the STM structure.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of simultaneously creating two, or more, trenches including first and second trenches adjoining each other in the first main surface of the semiconductor substrate and a trench of a dotted line form that is located along the outside of the two, or more, trenches wherein the plurality of first holes are arranged at intervals in a predetermined direction and that, thereby, has a surface pattern of a dotted line form in the first main surface, the step of ion implantation of the first impurities in order to form the first impurity region in each of the two sidewalls of the first trench and the step of ion implantation of the second impurities in order to form the second impurity region in each of the two sidewalls of the second trench, wherein the low concentration region is formed on both sidewalls of the trench of a dotted line form by means of an implantation at the same time as the ion implantation of the first or second impurities.
Thus, a trench of a dotted line form is used in a twin trench structure and, thereby, a high concentration region and a low concentration region can be simultaneously formed by means of a single ion implantation step so that simplification of the process can be achieved.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of creating a first group of trenches made of a plurality of first trenches in the first main surface of the semiconductor substrate, the step of ion implantation for forming the first impurity regions in the sidewalls on both sides of each of the first trenches, the step of creating a second group of trenches made of a plurality of second trenches in the first main surface so that the first trenches and the second trenches are located in an alternating manner, the step of ion implantation for forming the second impurity regions in the sidewalls on both sides of each of the second trenches and the step of the implantation of impurities of a conductive type opposite to that of the already implanted impurities into the sidewalls on both sides of the above described trench positioned at the outermost portion under the condition wherein the first and second trenches arranged in an alternating manner, except the trench located at the outermost portion, are filled in with a filling layer so as to substantially lower the concentration of the already implanted impurities so that the low concentration region is formed.
Thus, in the twin trench structure, the concentration of the impurities at the outermost portion of the repeating structure can be lowered by means of counter doping.
The above described manufacturing method for a semiconductor device is preferably provided with the step of creating a first trench group made of a plurality of first trenches in the first main surface of the above described semiconductor substrate, the step of ion implantation for forming the first impurity regions in the sidewalls on both sides of each of the first trenches, the step of creating a second group of trenches made of a plurality of second trenches in the first main surface under the condition wherein each of the first trenches is filled in with a filling layer so that the first trenches and the second trenches are located in an alternating manner, the step of ion implantation for forming the second impurity regions in the sidewalls on both sides of each of the second trenches, the step of creating a new trench at the outermost portion outside of the trench located at the outermost portion of the first and second trenches arranged in an alternating manner under the condition wherein each of the first and second trenches is filled in with a filling layer and the step of forming a low concentration region of which the impurity concentration is lower than that of the first or second impurity region by implanting impurity ions of the first or second conductive type.
Thus, in the twin trench structure, the trenches of the center portion and of the outermost portion in the repeating structure can be separately fabricated and ion implantations can also be separately carried out.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of simultaneously creating a first group of trenches made of a plurality of first trenches and a second group of trenches made of a plurality of second trenches in the first main surface of the semiconductor substrate so that the first trenches and the second trenches are located in an alternating manner, the step of ion implantation for forming the first impurity regions in the sidewalls on both sides of each of the plurality of first trenches forming the first group of trenches under the condition wherein the second group of trenches is filled in with a first filling layer, the step of ion implantation for forming the second impurity regions in the sidewalls on both sides of each of the plurality of second trenches forming the second group of trenches under the condition wherein the first group of trenches is filled in with a second filling layer and the step of implanting impurity ions of a conductive type opposite to the already implanted impurities into the sidewalls on both sides of the trench at the outermost portion under the condition wherein all of the trenches of the plurality of first trenches forming the first group of trenches and plurality of second trenches forming the second group of trenches, except the trench at the outermost portion, located at the outermost portion, are filled in with a third filling layer so as to lower the concentration of the already implanted impurities so that the low concentration region is formed.
Thus, in the bi-pitch implantation, the concentration of the impurity region of the outermost portion in the repeating structure can be lowered by means of counter doping.
The above described manufacturing method for a semiconductor device is preferably provided with the step of simultaneously creating a first group of trenches made of a plurality of first trenches and a second group of trenches made of a plurality of second trenches in the first main surface to semiconductor substrate so that the first trenches and the second trenches are located in an alternating manner, the step of ion implantation for forming the first impurity regions in the sidewalls on both sides of each of the plurality of first trenches forming the first group of trenches under the condition wherein the second group of trenches is filled in with a first filling layer and the step of ion implantation for forming the second impurity regions in the sidewalls on both sides of each of the plurality of second trenches forming the second group of trenches under the condition wherein the first group of trenches is filled in with a second filling layer, wherein the trench at the outermost portion, located at the outermost portion, from among the trenches of the plurality of first trenches forming the first group of trenches and the plurality of second trenches forming the second group of trenches is a trench of a dotted line form having a surface pattern of a dotted line form wherein a plurality of holes are arranged at intervals in a predetermined direction in the first main surface.
Thus, in the case that a bi-pitch implantation is used, a high concentration region and a low concentration region can be simultaneously formed through a single ion implantation step by using a trench of a dotted line form and, thereby, simplification of the process can be achieved.
The above described manufacturing method for a semiconductor device is preferably provided with the step of forming two, or more, trenches in the first main surface of the semiconductor substrate, the step of ion implantation of impurities for forming the first or second impurity regions in the sidewalls on one side of the two, or more, trenches and the step of ion implantation of impurities of the same conductive type as that of the already implanted impurities into the sidewalls on one side of the trenches, other than the trench located at the outermost portion, under the condition wherein the trench located at the outermost portion, from among the two, or more, trenches, is filled in with a filling layer so as to substantially increase the concentration of the already implanted impurities and, thereby, the above described first or second impurity regions in the sidewalls of the trench located at the outermost portion becomes a region of a comparatively low concentration.
Thus, in the STM structure, ion implantation of impurities of the same conductive type is again carried out in the sidewalls of the trenches of the center portion and, thereby, the impurity concentration of the center portion is enhanced so that the concentration of the impurity regions at the outermost portion of the repeating structure can be made to be of a comparatively low concentration.
The above described manufacturing method for a semiconductor device is preferably further provided with the step of creating a first group of trenches made of a plurality of first trenches in the first main surface of the semiconductor substrate, the step of ion implantation for forming the first impurity regions in the sidewalls on both sides of each of the first trenches, the step of forming a second group of trenches made of a plurality of second trenches in first main surface so that the first trenches and the second trenches are located in an alternating manner, the step of ion implantation for forming the second impurity regions in the sidewalls on both sides of each of the second trenches and the step of implanting impurities of the same conductive type as the already implanted impurities in the sidewalls on both sides of the trenches, other than the trench located at the outermost portion, under the condition wherein the trench located at the outermost portion, from among the first and second trenches arranged in an alternating manner is filled in with a filling layer so as to substantially increase the concentration of the already implanted impurities so that the first or second impurity regions in the sidewalls of the trench located at the outermost portion becomes a region of a comparatively low concentration.
Thus, in the twin trench structure, ion implantation of impurities of the same conductive type is again carried out in the sidewalls of the center portion and, thereby, the impurity concentration of the center portion is enhanced so that the concentration of the impurity region at the outermost portion of the repeating structure can be lowered to have a comparatively low concentration.
The above described manufacturing method for a semiconductor device preferably is further provided with the step of simultaneously creating a first group of trenches made of a plurality of first trenches and a second group of trenches made of a plurality of second trenches in the first main surface of the semiconductor substrate so that the first trenches and second trenches are located in an alternating manner, the step of ion implantation for forming the first impurity regions in the sidewalls on both sides of each of the plurality of first trenches forming the first group of trenches under the condition wherein the second group of trenches is filled in with a first filling layer, the step of ion implantation for forming the second impurity regions in the sidewalls on both sides of each of the plurality of second trenches forming the second group of trenches under the condition wherein the first group of trenches is filled in with a second filling layer and the step of implanting impurity ions of the same conductive type as that of the already implanted impurities in the sidewalls on both sides of the trenches other than the trench at the outermost portion under the condition wherein the trench at the outermost portion, located at the outermost portion, from among the plurality of first trenches forming the first group of trenches and the plurality of second trenches forming the second group of trenches is filled in with a third filling layer so as to enhance the concentration of the already implanted impurities so that the first or second impurity regions in the sidewalls of the trench at the outermost portion become regions of a comparatively low concentration.
Thus, in the bi-pitch implantation, ion implantation of impurities of the same conductive type is again carried out in the sidewalls of the trenches in the center portion and, thereby, the impurity concentration of the center portion is enhanced so that the impurity region at the outermost portion of the repeating structure can be made to have a comparatively low concentration.